A reactor pressure vessel (RPV) in a light water reactor, such as a boiling water reactor (BWR), typically includes a core shroud surrounding the nuclear fuel core and supported by a shroud support structure. FIG. 1 is a partial sectional view, with parts cut-away, of a related-art RPV 20 for a BWR. RPV 20 has a generally cylindrical shape and is closed at one end by a bottom head (not shown) and at its other end by removable top head (not shown). A top guide (not shown) is spaced above a core plate 22 within RPV 20. A shroud 24 surrounds core plate 22 and is supported by a shroud support structure 26. An annulus 28 is formed between shroud 24 and sidewall 30 of RPV 20.
An inlet nozzle 32 extends through sidewall 30 of RPV 20 and is coupled to a jet pump assembly 34. The hollow tubular jet pumps in the shroud annulus provide the required reactor core water flow. Jet pump assembly 34 includes a riser pipe 38, a plurality of inlet mixers 42 that make up the upper portion of the jet pump and are connected to a plurality of riser pipes 38 by a plurality of transition assemblies 44, and a diffuser 46. Each inlet mixer 42 is laterally positioned and supported against two opposing rigid contacts within restrainer brackets that support inlet mixer 42 by attaching to adjacent jet pump riser pipe 38. Riser pipe 38 extends between and substantially parallel to shroud 24 and RPV sidewall 30. A slip joint 48 couples each inlet mixer 42 to a corresponding diffuser 46, which is the lower portion of the jet pump. Slip joint 48 between jet pump inlet mixer 42 and jet pump diffuser 46 has about 0.015 inch operating clearance to accommodate relative axial thermal expansion movement between the upper and lower parts of the jet pump, which results in leakage flow from the driving pressure inside the pump.
FIG. 2 is a partial side view, with parts cut away, of related-art slip joint 48. Inlet mixer 42 is generally cylindrical and includes an outer surface 50. Inlet mixer 42 is received in diffuser 46. Diffuser 46 includes an inner surface 52 positioned adjacent to inlet mixer outer surface 50. Operational clearance 54 is shown at an interface 56 between inlet mixer outer surface 50 and diffuser inner surface 52. A diffuser guide ear 45 projects outward from a top of diffuser 46 to provide proper alignment between diffuser 46 and inlet mixer 42. Several guide ears 45 may be positioned about a top perimeter edge of diffuser 46, for example, four guide ears 45, at 90 degree intervals.
Slip joint 48 may be stainless steel in inlet mixer outer surface 50 with a cobalt alloy hardfacing extending over interface 56. Diffuser inner surface 52 may also be stainless steel, with only localized areas of cobalt alloy hardfacing extending into interface 56.